The journalist Peter Harvey, who has died of cancer aged 68, was a household name in Australia, where he worked for Channel Nine news as chief political reporter and news director. Yet one of the highest points of his career came at the Guardian in London in the early 1970s.

Born in Sydney, he began his career on the city's Daily Telegraph newspaper. He came to the Guardian from the US magazine Newsweek, where he had been reporting on the Vietnam war, and applied for a job in our newsroom. I took him on after he demonstrated his newsgathering talents with an exclusive story about the London Underground. He followed this up with a series of top news stories, helping to put the Guardian in the frontline of news competition in Fleet Street, after its move from the original Manchester headquarters to London.

Covering a routine press conference with the Liberal MP John Pardoe, he was told about information from government and private sources that was being acquired secretly by an inquiry agent and sold on. He immediately followed it up and spent days tracking down the agent. The man demonstrated how, by asking friendly contacts in the ministries, the Inland Revenue and other departments, he could get the information his clients were seeking.

Days of checking and counter-checking the story followed. The Guardian editor at the time, Alastair Hetherington, demanded a final test before allowing the story to go in – he asked for the details of his own taxes from the Inland Revenue. The agent delivered the information and the story led the paper next day.

Harvey was phoned by the attorney general at home early the next morning. There were questions in the house and to the editor from the prime minister, Edward Heath, who told Hetherington he might have to go to prison if he did not name the source, which the Guardian refused to do. Two Scotland Yard detectives were deputed to shadow Harvey, Hetherington and the news desk team in an effort to find the source. They did not have Harvey's skill but eventually the agent was tracked down and spent time in prison. The story brought Harvey a National Press award in 1973 as news reporter of the year, but he carried his successes quietly.

He then returned to Australia. He won many awards, including the Centenary medal for services to journalism in 2001. He is survived by his wife, Anne, and their two children, Claire and Adam, both journalists.